1. Technical Field
The present disclosure relates to an intelligent power module (IPM) and a related assembling method.
The disclosure refers, in particular, but not exclusively, to an intelligent power module comprising a control circuit board and a power circuit board as well as a body case closed by a lid in order to package the boards, and the following description is made with reference to this field of application for convenience of explanation only.
2. Description of the Related Art
As is known, in the technical field of the power modules, intelligent power modules (IPM) combine application-specific insulated-gate bipolar transistors (IGBTs) and diodes, control functions, smart protections and extra optional features.
In recent years, the use of intelligent power modules has rapidly increased, in particular in motor drive applications, thanks to the benefits of greater integration levels. In this field, for instance, an intelligent power module may be connected to a microcontroller in order to convert the microcontroller output into the correct high-power waveform to drive a motor. In particular, intelligent power modules are advanced hybrid power devices designed to integrate high speed and low loss IGBTs with dedicated drive circuitry for AC motor control, usually implemented on a printed circuit board (PCB).
In its more general form, an intelligent power module usually comprises a power portion in the form of a power circuit board, comprising power devices, and a control portion in the form of a control circuit board for the driving and monitoring of the power circuit board, such as a gate driver printed circuit board (PCB) for driving the power devices of the power circuit board. In particular, the gate driver PCB may be located on a direct-bond copper (DBC) substrate.
Naturally, it is desired to electrically connect the control circuit board and the power circuit board by means of bonds that introduce low values of resistance, and withstand—without melting—the passage of high currents, in the range of 150-200 A. This desire is particularly felt in the case of so-called power packages, which are commonly used for packaging integrated circuits that form devices with high current consumption, such as for example power diodes, low-voltage power MOSFETs, or else insulated-gate bipolar transistors (IGBTs).
Concerning the electrical connections between the control circuit board and the power circuit board of the intelligent power module, it is well known that they are commonly realized either through wire-bonding or clip-bonding techniques.
By way of example, FIG. 1 is a schematic illustration of an intelligent power module (IPM) 1 realized according to the prior art.
The intelligent power module 1 comprises:                a power circuit board 2, in turn including power devices, such as switches, globally indicated with 3; the power devices 3 are provided on a substrate, in particular a direct copper bond substrate 4; and        a control circuit board 5, in particular a gate driver PCB, for driving the power circuit board 2, the control circuit board 5 in turn including gate driver components 6 and at least a logic block 7.        
In particular, the control circuit board 5 is connected to the power devices 3 by appropriate bonding wires 8. Both the control circuit board 5 and the power circuit board 2 are protected by a protective case or package, formed by:                a base plate 9, to which a radiating heat sink, not shown in the figure, is also normally attached;        a case body 10; and        a lid 11, usually made of an insulating material, the lid closing the case body and thus completing a package of the intelligent power module 1.        
The case body 10 comprises leads 12 located at its periphery in dedicated positions of its internal walls. The leads 12 are connected to the control circuit board 5 through bonding wires 13 to enable proper operation of the power circuit board 2 and of the electronic circuits provided therein. The leads 12 have connection terminals which exit from the lid 11 through suitable holes provided at the periphery of the lid 11 itself, enabling the connection of the control circuit board 5 to the outside world.
For the purpose of connection between the power circuit board 2 and the control circuit board 5 and between the control circuit board 5 and the external world, among other techniques, bonding wires or clips bonding may be used.
As regards to the wire bonding technique, it is likewise possible to distinguish between thin-wire bonding and heavy-wire bonding; in either case, the bonding is carried out by means of a wire-like connection element of conductive material, usually having a circular section.
As regards to the clip bonding technique, the bonding is carried out by means of so-called clips, i.e., strips of conductive material (typically, copper), so as to obtain an almost planar connection element of conductive material.
For the assembly of an intelligent power module, the control circuit board may be a generic printed circuit board comprising at least a logic block. In particular, as it is known, the logic block comprises electrical components that are put into the printed circuit board and interconnected to each other using any one of the following different technologies:                the “through holes” technology, in which the printed circuit board is manufactured with plated through holes; these holes are used as references for placing the electrical components which, once installed, may be soldered into position using either manually, wave- or reflow-soldering techniques. In this case, small connectors may be packaged on a tape and reel for surface mount device placement by standard pick and place machines;        the “surface mounted” technology, also known as Surface Mount Device (SMD) technology, in which, before the electrical components are placed on the printed circuit board, solder paste is applied to the pads of the component and/or the board itself; the board is then passed through a solder reflow oven; or        the “press-fit” technology, in which pins of press-fit connectors are pressed into metalized, namely plated, through-holes in the printed circuit board by applying a mechanical force; due to the high radial pressure, the press-fit pins are deformed, when pressed in the holes, resulting in a gas-tight electrical connection between each press-fit pin and the corresponding metalized through-hole.        
In their more general form, the press-fit connectors comprise an elastic core acting as a spring and are tin plated for enhancing the electrical contact performance; they may have different shapes. It should be underlined that press-fit pins, due to their elastic and conductive features, may thus ensure good mechanical stability and electrical contact.
By way of example, FIGS. 2A and 2B are schematic illustration of a press-fit connector 14 of the known type. More in particular, the press-fit connector 14 comprises a tubular body 15 and a needle 16 having at least one eye 17 so as to act as a spring core, and a metal plating layer 18A, in particular a copper layer, provided outside the needle 16. Another metal plating layer 18B is provided on the walls of a suitable hole 20 in a PCB 19 for receiving the needle 16 of the press-fit connector 14.
It is also well known that, according to the known method of assembling intelligent power modules, the control circuit board is located inside the case body, over the power circuit board, and molded to the case body by an epoxy resin using a molding process.
Due to this architecture, the known intelligent power modules show different problems, mainly tied to the huge number of bonding wires to be suitably placed inside the case body thereof in order to ensure multiple interconnections between the different elements composing the module itself.
Moreover, the use of such bonding wires also involves different disadvantages such as:
(a) the module has a low input/output count due to the limitations of the wire bonding technology,
(b) the module needs to be provided with large bonding pads, that are also at a sufficient distance (pitch) one another,
(c) relatively large quantities of gold are involved in the assembling process,
(d) the assembling process shows a low production rate,
(e) the connection provided by wire bonding has relatively poor electrical performance,
(f) difficulties arise, when variations in bond geometry are needed, and
(g) robustness and reliability problems are brought about by environmental conditions.
In addition, both the wire bonding and the clip bonding involve a very high assembly complexity.
Moreover, according to the prior art solutions, any time the control circuit has to be changed, for instance based on a new desired/required electronic function, a new dedicated intelligent power module has to be fabricated, with an evident impact on the production costs.